TRAIL (TNF Related Apoptosis-Inducing Ligand, Apo-2L), a member of the Tumor Necrosis Factor supergene family, has multiple functions that include induction of apoptosis and regulation of a host of cellular genes. This potent cytokine is synthesized in many types of cells; the response of a TRAIL-exposed cell is dependent upon which among the five TRAIL receptors it expresses. The results of earlier studies in our laboratory were consistent with a role for TRAIL in placental immune privilege. We found that trophoblast-derived tumor cells express a decoy receptor, DcR1, and are not killed by recombinant TRAIL. Preliminary studies for this proposal demonstrate that TRAIL and its receptors are differentially expressed among the cells at the early human implantation site. The patterns of expression suggest roles in immune privilege as well as regulation of genes important to column formation and trophoblast migration. Microarray analyses of cDNA from term cytophoblast cells support these latter possibilities, demonstrating that TRAIL diminishes certain integrins, growth factors and growth factor receptors.. Relationships with pathological conditions of fertility are implied by our finding that the TRAIL gene has four allelic variants in the 3' UTR that could affect message stability. In this research we focus on functional aspects of TRAIL at the early human implantation site. The Specific Aims of the research are: Aim 1: To assess the role of TRAIL and TRAIL-R in defending the early placenta against blood-born maternal immune cells; Aim 2: To determine the role of TRAIL in trophoblast migration; Aim 3: To establish the effect on TRAIL on trophoblast expression of the HLA class Ib gene HLA-G; Aim 4: To initiate studies on the ability of recombinant TRAIL to alter the expression of trophoblast genes using cDNA microarray analysis. We expect the results of this research to have a major impact on our understanding of the molecular basis for cell-to-cell interactions during implantation and early placentation that will ultimately lead to better therapies for improving fertility and reproductive performance.